In Search of Better Load Ratings

Typically, engineers must make a number of subjective assumptions regarding loading and response behavior when they develop a load rating for civil structures. As a result, many unknowns may remain about the actual behavior of both new and older structures. Field measurements, collected by nondestructive testing equipment, can be integrated into these theoretical models, resulting in more accurate load ratings. The goal is to make feasible the evaluation of infrastructure on a routine basis. A field testing system and set of procedures has been developed which allow the test to be completed in a fraction of the time needed for traditional tests. The system has been used on shuttle bridge at the Miami International Airport, on U.S. Army Corps of Engineers' lock and dams projects and on various highway and railroad bridges, with limited shutdown of infrastructure operation. Public works agencies have several reasons for conducting these field tests. The first simply is to track deterioration over a number of years. The second is to help them prioritize future inspections. A final reason is to help states determine if overload permits may be granted.